feat(backend): add LocationService

- Add LocationService to manage LocationSource per user
- Add UserNotFoundError for generic user-related errors
- updateUserLocation throws if source not initialized

Co-authored-by: Ona <no-reply@ona.com>

apps/aris-backend/src/lib/error.ts

@@ -0,0 +1,8 @@
+export class UserNotFoundError extends Error {
+	constructor(
+		public readonly userId: string,
+		message?: string,
+	) {
+		super(message ? `${message}: user not found: ${userId}` : `User not found: ${userId}`)
+	}
+}

apps/aris-backend/src/location/service.test.ts

@@ -0,0 +1,111 @@
+import { describe, expect, test } from "bun:test"
+
+import { UserNotFoundError } from "../lib/error.ts"
+import { LocationService } from "./service.ts"
+
+describe("LocationService", () => {
+	test("feedSourceForUser creates source on first call", () => {
+		const service = new LocationService()
+		const source = service.feedSourceForUser("user-1")
+
+		expect(source).toBeDefined()
+		expect(source.id).toBe("location")
+	})
+
+	test("feedSourceForUser returns same source for same user", () => {
+		const service = new LocationService()
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).toBe(source2)
+	})
+
+	test("feedSourceForUser returns different sources for different users", () => {
+		const service = new LocationService()
+		const source1 = service.feedSourceForUser("user-1")
+		const source2 = service.feedSourceForUser("user-2")
+
+		expect(source1).not.toBe(source2)
+	})
+
+	test("updateUserLocation updates the source", () => {
+		const service = new LocationService()
+		const source = service.feedSourceForUser("user-1")
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		service.updateUserLocation("user-1", location)
+
+		expect(source.lastLocation).toEqual(location)
+	})
+
+	test("updateUserLocation throws if source does not exist", () => {
+		const service = new LocationService()
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		expect(() => service.updateUserLocation("user-1", location)).toThrow(UserNotFoundError)
+	})
+
+	test("lastUserLocation returns null for unknown user", () => {
+		const service = new LocationService()
+
+		expect(service.lastUserLocation("unknown")).toBeNull()
+	})
+
+	test("lastUserLocation returns last location", () => {
+		const service = new LocationService()
+		service.feedSourceForUser("user-1")
+		const location1 = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+		const location2 = {
+			lat: 52.0,
+			lng: -0.2,
+			accuracy: 5,
+			timestamp: new Date(),
+		}
+
+		service.updateUserLocation("user-1", location1)
+		service.updateUserLocation("user-1", location2)
+
+		expect(service.lastUserLocation("user-1")).toEqual(location2)
+	})
+
+	test("removeUser removes the source", () => {
+		const service = new LocationService()
+		service.feedSourceForUser("user-1")
+		const location = {
+			lat: 51.5074,
+			lng: -0.1278,
+			accuracy: 10,
+			timestamp: new Date(),
+		}
+
+		service.updateUserLocation("user-1", location)
+		service.removeUser("user-1")
+
+		expect(service.lastUserLocation("user-1")).toBeNull()
+	})
+
+	test("removeUser allows new source to be created", () => {
+		const service = new LocationService()
+		const source1 = service.feedSourceForUser("user-1")
+
+		service.removeUser("user-1")
+		const source2 = service.feedSourceForUser("user-1")
+
+		expect(source1).not.toBe(source2)
+	})
+})

apps/aris-backend/src/location/service.ts

@@ -0,0 +1,55 @@
+import { LocationSource, type Location } from "@aris/source-location"
+
+import { UserNotFoundError } from "../lib/error.ts"
+
+/**
+ * Manages LocationSource instances per user.
+ */
+export class LocationService {
+	private sources = new Map<string, LocationSource>()
+
+	/**
+	 * Get or create a LocationSource for a user.
+	 * @param userId - The user's unique identifier
+	 * @returns The user's LocationSource instance
+	 */
+	feedSourceForUser(userId: string): LocationSource {
+		let source = this.sources.get(userId)
+		if (!source) {
+			source = new LocationSource()
+			this.sources.set(userId, source)
+		}
+		return source
+	}
+
+	/**
+	 * Update location for a user.
+	 * @param userId - The user's unique identifier
+	 * @param location - The new location data
+	 * @throws {UserNotFoundError} If no source exists for the user
+	 */
+	updateUserLocation(userId: string, location: Location): void {
+		const source = this.sources.get(userId)
+		if (!source) {
+			throw new UserNotFoundError(userId)
+		}
+		source.pushLocation(location)
+	}
+
+	/**
+	 * Get last known location for a user.
+	 * @param userId - The user's unique identifier
+	 * @returns The last location, or null if none exists
+	 */
+	lastUserLocation(userId: string): Location | null {
+		return this.sources.get(userId)?.lastLocation ?? null
+	}
+
+	/**
+	 * Remove a user's LocationSource.
+	 * @param userId - The user's unique identifier
+	 */
+	removeUser(userId: string): void {
+		this.sources.delete(userId)
+	}
+}